Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades are the primary elements for converting wind energy into electrical energy. The blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between its sides. Consequently, a lift force, which is directed from the pressure side towards the suction side, acts on the blade. The lift force generates torque on the main rotor shaft, which is connected to a generator for producing electricity.
The amount of power that may be produced by a wind turbine is typically limited by structural limitations (i.e. design loads) of the individual wind turbine components. For example, the blade root of a wind turbine may experience loads associated with both average loading due to turbine operation and dynamically fluctuating loads due to environmental conditions. For example, during operation, the blade may experience blade root reactions as well as span-wise loading that may lead to damaging strain and/or buckling of the rotor blade. The fluctuating loads can change day-to-day or season-to-season and may be based on wind speed, wind peaks, wind turbulence, wind shear, changes in wind direction, density in the air, yaw misalignment, upflow, or similar.
It is imperative to wind turbine operation to ensure loads acting on the turbine do not exceed design margins. The term “margin” or similar as used herein generally refers to a predetermined maximum allowable load such that any additional load above the predetermined load would cause a deformation (e.g. strain or buckling) to the wind turbine component. Thus, many wind turbines employ one or more sensors configured to measure the loads acting on the various wind turbine components. Though the sensors may provide the desired information, new sensor systems can be complex and expensive to install. Further, the sensors may provide inaccurate information and can be prone to fail.
Additionally, wind turbines utilize control systems configured to estimate loads acting on the wind turbine based on a wind turbine thrust. The terms “thrust,” “thrust value,” “thrust parameter” or similar as used herein are meant to encompass a force acting on the wind turbine due to the wind. The thrust force comes from a change in pressure as the wind passes the wind turbine and slows down. Such control strategies estimate loads acting on the wind turbine by determining an estimated thrust using a plurality of turbine operating conditions, such as, for example, pitch angle, power output, generator speed, and air density. The operating conditions are inputs for the algorithm, which includes a series of equations, one or more aerodynamic performance maps, and one or more look-up tables (LUTs). For example, the LUT may be representative of a wind turbine thrust. A +/− standard deviation of the estimated thrust may also be calculated, along with an operational maximum thrust and a thrust limit. As such, the wind turbine may be controlled based on a difference between the maximum thrust and the thrust limit.
In view of the foregoing, the art is continuously seeking new and improved systems for estimating loads acting on a wind turbine. More specifically, a system and method for operating a wind turbine based on estimated blade margins would be desired in the art. Further, a system and method that incorporated existing hardware and software would be advantageous.